In production of semiconductor devices, micro-fabrication is generally carried out according to lithographic techniques by use of photoresist. The process of micro-fabrication comprises the steps of: forming a thin photoresist layer on a semiconductor substrate such as a silicon wafer; covering the layer with a mask pattern corresponding to the aimed device pattern; exposing the layer to active light such as UV light through the mask pattern; developing the exposed layer to obtain a photoresist pattern; and etching the substrate by use of the photoresist pattern as a protective film, to form a fine relief corresponding to the above pattern. Since integration degree of semiconductor devices has been increased recently, the step of exposure tends to be carried out by use of light of very short wavelength, such as KrF excimer laser light (wavelength: 248 nm), ArF excimer laser light (wavelength: 193 nm) or extreme UV light (wavelength: 13.5 nm). The above photolithographic process, however, often suffers from a problem of dimension precision degradation of the photoresist pattern. The dimension precision degradation is caused by a standing wave of light reflected from the substrate and/or by diffused reflection of the exposure light due to roughness of the substrate. Further, the resist layer may be adversely effected by gases given off from the substrate placed thereunder if the exposure is performed by use of light of very short wavelength, such as extreme UV light. To cope with those problems, many researchers are studying about a bottom anti-reflective coating provided between the photoresist layer and the substrate. The bottom anti-reflective coating is required to have various properties. For example, it is preferred for the bottom anti-reflective coating to largely absorb radiation used for exposure of the photoresist, to prevent diffuse reflection and the like so that the exposed and developed photoresist can have a cross section perpendicular to the substrate surface, and to be insoluble in solvents contained in the photoresist composition (namely, not to cause intermixing). The intermixing is particularly serious because it often gives adverse effects to the interface between the photoresist layer and the bottom anti-reflective coating. Accordingly, the intermixing is liable to make it difficult to control the pattern or shape of the photoresist.
The bottom anti-reflective coating is often formed from a thermo-crosslinkable composition, so as to prevent intermixing with the photoresist applied thereon. Consequently, the formed coating is generally insoluble in an alkaline developing solution used for development of the photoresist. Accordingly, in general, the anti-reflective coating must be removed by dry-etching before fabrication of the semiconductor substrate (see, for example, Patent document 1).
However, when the coating is removed by dry-etching, the photoresist tends to be partly removed together with the coating. This makes it difficult to keep enough thickness of the photoresist to fabricate the substrate.
In view of this, it is desired to develop a bottom anti-reflective coating which is sufficiently soluble in an alkaline developing solution used for development of the photoresist and hence which can be developed and removed together with the photoresist. In order to meet this desire, researchers have studied the bottom anti-reflective coating developable and removable together with the photoresist, wherein the pattern is formed in the photoresist and the bottom anti-reflective coating.
For example, methods are proposed in which reactions between dienes and dienophiles are made to form bottom anti-reflective coatings developable and removable together with the photoresist (Patent documents 2 to 4). However, if those methods are adopted, it is often the case that the coating is still not crosslinked when the photoresist composition is spread thereon and, as a result, the coating is liable to intermix with the photoresist layer. In order to avoid the intermixing, the solvent of the photoresist composition must be selected not to dissolve the bottom anti-reflection coating. Accordingly, since usable photoresists are restricted depending on the selected solvent, there is a problem of lacking versatility.